LMTK3 Represses Tumor Suppressor-like Genes through Chromatin Remodeling in Breast Cancer

A revised nomenclature for the lemur family of protein kinases

The lemur family of protein kinases has gained much interest in recent years as they are involved in a variety of cellular processes including regulation of axonal transport and endosomal trafficking, modulation of synaptic functions, memory and learning, and they are centrally placed in several intracellular signalling pathways. Numerous studies have also implicated role of the lemur kinases in the development and progression of a wide range of cancers, cystic fibrosis, and neurodegenerative diseases. However, parallel discoveries and inaccurate prediction of their kinase activity have resulted in a confusing and misleading nomenclature of these proteins. Herein, a group of international scientists with expertise in lemur family of protein kinases set forth a novel nomenclature to rectify this problem and ultimately help the scientific community by providing consistent information about these molecules.

Development and Verification of a Prognostic Stemness-Related Gene Signature in Triple-Negative Breast Cancer

Background. It is well known that cancer stem cells can induce cancer metastasis, which causes the majority of cancer-related death, especially in triple-negative breast cancer (TNBC). TNBC features a high metastatic rate and low metastasis-free survival and is regarded as the most malignant subtype of breast cancer. The purpose of this study is to explore prognostic biomarkers that can predict metastasis of triple-negative breast cancer. Methods. The human triple-negative breast cancerSUM149PT cells were used for the study. The cancer stem cell spheres (sum149-Stem) and paired adherent cancer cells (sum149-Tumor) were collected to extract total RNAs. RNA-seq was used to analysis the mRNA expression of cancer stem cells and paired adherent cancer cells. Two different gene expression omnibus datasets (https://www.ncbi.nlm.nih.gov/gds), GSE58812 and GSE33926, were used to explore the mechanism of different expression genes between stem cells and adherent cancer cells. Seven genes showed prognostic function in all datasets. The STITCH database (https://www.stitchdata.com/) was used to explore the possible metastasis-inhibiting drugs that can target the seven genes. Each gene expression was compared by Pearson analysis. The receiver operating characteristic curve (ROC) and Kaplan–Meier survival curve were performed to assess the metastasis prognostic ability of the seven-gene modeling two different GEO datasets. Results. A subset of 7 stemness-related genes (SRGs) containing UCN, ST3GAL5, FDPS, HK2, MALL, LMTK3, and CRHR2 were identified in three independent cohorts. Univariate Cox analysis showed that ST3GAL5 plays an antitumor role in TNBC metastasis, and the other 6 genes promote the metastatic progression of TNBC. The ability of the 7-SRGs gene Cox model to predict TNBC metastasis was constructed with the GSE58812 dataset. Most of the genes showed significant expression in patients with different risk levels. Additionally, the model showed predictive value in another GEO dataset of TNBC patients. ROC curves indicated that the seven-gene model has a significant predictive value of TNBC metastasis. Conclusions. Expression analysis of the 7-SRGs signature model at diagnosis has predictive value for metastasis in TNBC patients.

The Inhibitory Properties of a Novel, Selective LMTK3 Kinase Inhibitor

Recently, the oncogenic role of lemur tyrosine kinase 3 (LMTK3) has been well established in different tumor types, highlighting it as a viable therapeutic target. In the present study, using in vitro and cell-based assays coupled with biophysical analyses, we identify a highly selective small molecule LMTK3 inhibitor, namely C36. Biochemical/biophysical and cellular studies revealed that C36 displays a high in vitro selectivity profile and provides notable therapeutic effect when tested in the National Cancer Institute (NCI)-60 cancer cell line panel. We also report the binding affinity between LMTK3 and C36 as demonstrated via microscale thermophoresis (MST). In addition, C36 exhibits a mixed-type inhibition against LMTK3, consistent with the inhibitor overlapping with both the adenosine 5'-triphosphate (ATP)- and substrate-binding sites. Treatment of different breast cancer cell lines with C36 led to decreased proliferation and increased apoptosis, further reinforcing the prospective value of LMTK3 inhibitors for cancer therapy.

The Relationship Between the Network of Non-coding RNAs-Molecular Targets and N6-Methyladenosine Modification in Colorectal Cancer

Recent accumulating researches implicate that non-coding RNAs (ncRNAs) including microRNA (miRNA), circular RNA (circRNA), and long non-coding RNA (lncRNAs) play crucial roles in colorectal cancer (CRC) initiation and development. Notably, N6-methyladenosine (m⁶A) methylation, the critical posttranscriptional modulators, exerts various functions in ncRNA metabolism such as stability and degradation. However, the interaction regulation network among ncRNAs and the interplay with m⁶A-related regulators has not been well documented, particularly in CRC. Here, we summarize the interaction networks and sub-networks of ncRNAs in CRC based on a data-driven approach from the publications (IF > 6) in the last quinquennium (2016–2021). Further, we extend the regulatory pattern between the core m⁶A regulators and m⁶A-related ncRNAs in the context of CRC metastasis and progression. Thus, our review will highlight the clinical potential of ncRNAs and m⁶A modifiers as promising biomarkers and therapeutic targets for improving the diagnostic precision and treatment of CRC.

Knockdown of LMTK3 in the Endometrioid Adenocarcinoma Cell Line Ishikawa: Inhibition of Growth and Estrogen Receptor α

Objective

The curative effect of high-efficiency progesterone and other therapeutic drugs for endometrioid adenocarcinoma patients with preservation of reproductive capacity has not been satisfactory so far. Novel therapeutic drugs need to be explored.

Methods

We investigated the cytoplastic and nuclear expression levels of LMTK3 between endometrioid adenocarcinoma tissues and adjacent endometrial tissues by immunohistochemistry. We detected the effects of LMTK3 on cell viability of Ishikawa cells by CCK-8. We detected the effects of LMTK3 on cell cycle and apoptosis of Ishikawa cells by flow cytometry. We also detected the effects of LMTK3 knockdown on mRNA and protein levels of ERα by qRT-PCR and western blotting, respectively. We also used the cBioPortal online database to analyze the coexpression of LMTK3 and ESR1 in 1647 UCEC samples.

Results

We used TMAs to identify that LMTK3 was mainly detected in the cytoplasm of endometrioid tissues, and cytoplasmic LMTK3 expression in endometrioid tissues was higher than that in adjacent endometrial tissues (P < 0.05). LMTK3 knockdown decreased the proliferation of Ishikawa cells through decreasing cell viability (P < 0.01), increasing G1 (P < 0.001) arrest, and promoting apoptosis (P < 0.01). There was a positive correlation between the mRNA expression levels of LMTK3 and ESR1 (Spearman: P=2.011e-5, R=0.13; Pearson: P=7.18e-8, R=0.17). Knockdown of LMTK3 also reduced the mRNA (P < 0.001) and protein (P < 0.001) levels of ERα.

Conclusions

Inhibitors of LMTK3 may be a possible future treatment for ERα and LMTK3 highly expressed endometrioid adenocarcinoma following appropriate studies.

Lemur tyrosine kinase-3 (LMTK3) induces chemoresistance to cetuximab in colorectal cancer via the ERK/MAPK pathway

As an oncogenic kinase in multiple cancers, LMTK3 was deeply implicated in cancer pathogenesis. Nevertheless, its biological function in colorectal cancer (CRC) is still unclear. In this study, LMTK3 mRNA expression was assessed by RT-qPCR. LMTK3, phospho-ERK1/2 (p-ERK1/2), ERK1/2, and cleaved caspase-3 protein levels were detected by western blotting. Cetuximab (CTX)-resistant CRC cell models were constructed to investigate the mechanism of LMTK3-regulated CTX resistance in CRC. CTX half-maximal inhibitory concentration (IC₅₀), viability, apoptosis, cell cycle, migration, and invasion of CRC cells were analyzed via Cell Counting Kit-8 (CCK-8), flow cytometry, wound healing, and transwell assays. We found LMTK3 was distinctly upregulated in CRC tissues and cells, particularly in CTX-resistant CRC tissues and cells. LMTK3 inhibition lowered CTX half-maximal inhibitory concentration (IC₅₀) value, inhibited cell viability, induced cell apoptosis, triggered cell-cycle arrest, and impaired cell metastatic capability in CTX-resistant CRC cells. Moreover, we also demonstrated that LMTK3 induced CTX resistance in CRC via the activation of ERK/MAPK signaling in vitro. These results suggested a novel molecular mechanism by which LMTK3 participates in the development of CTX resistance in CRC.

The multifaceted role of lemur tyrosine kinase 3 in health and disease

In the last decade, LMTK3 (lemur tyrosine kinase 3) has emerged as an important player in breast cancer, contributing to the advancement of disease and the acquisition of resistance to therapy through a strikingly complex set of mechanisms. Although the knowledge of its physiological function is largely limited to receptor trafficking in neurons, there is mounting evidence that LMTK3 promotes oncogenesis in a wide variety of cancers. Recent studies have broadened our understanding of LMTK3 and demonstrated its importance in numerous signalling pathways, culminating in the identification of a potent and selective LMTK3 inhibitor. Here, we review the roles of LMTK3 in health and disease and discuss how this research may be used to develop novel therapeutics to advance cancer treatment.

The structure-function relationship of oncogenic LMTK3

Elucidating signaling driven by lemur tyrosine kinase 3 (LMTK3) could help drug development. Here, we solve the crystal structure of LMTK3 kinase domain to 2.1Å resolution, determine its consensus motif and phosphoproteome, unveiling in vitro and in vivo LMTK3 substrates. Via high-throughput homogeneous time-resolved fluorescence screen coupled with biochemical, cellular, and biophysical assays, we identify a potent LMTK3 small-molecule inhibitor (C28). Functional and mechanistic studies reveal LMTK3 is a heat shock protein 90 (HSP90) client protein, requiring HSP90 for folding and stability, while C28 promotes proteasome-mediated degradation of LMTK3. Pharmacologic inhibition of LMTK3 decreases proliferation of cancer cell lines in the NCI-60 panel, with a concomitant increase in apoptosis in breast cancer cells, recapitulating effects of LMTK3 gene silencing. Furthermore, LMTK3 inhibition reduces growth of xenograft and transgenic breast cancer mouse models without displaying systemic toxicity at effective doses. Our data reinforce LMTK3 as a druggable target for cancer therapy.

LMTK3 promotes tumorigenesis in bladder cancer via the ERK/MAPK pathway

Lemur tyrosine kinase 3 (LMTK3) is a key member of the serine–threonine tyrosine kinase family. It plays an important role in breast cancer tumorigenesis and progression. However, its biological role in bladder cancer remains elusive. In this study, we demonstrated that LMTK3 was overexpressed in bladder cancer and was positively correlated with bladder cancer malignancy. High LMTK3 expression predicted poor overall survival. Knockdown of LMTK3 in bladder cancer cells triggered cell‐cycle arrest at G2/M phase, suppressed cell growth, and induced cell apoptosis in bladder cancer cells. Furthermore, Transwell assays revealed that reduction of LMTK3 decreased cell migration by regulating the epithelial‐to‐mesenchymal transition pathway. Conversely, LKTM3 overexpression was shown to promote proliferation and migration of bladder cancer cells. We assessed phosphorylation of MEK and ERK1/2 in bladder cancer cells depleted of LMTK3 and demonstrated a reduced phosphorylation status compared with the control group. Using an MAPK signaling‐specific inhibitor, U0126, we could rescue the promotion of proliferation and viability in LMTK3‐overexpressing cells. In conclusion, we extend the status of LMTK3 as an oncogene in bladder cancer and provide evidence for its function via the activation of the ERK/MAPK pathway. Thus, targeting LMTK3 may hold potential as a diagnostic and prognostic biomarker and as a possible future treatment for bladder cancer.

Discovery of cyclic guanidine-linked sulfonamides as inhibitors of LMTK3 kinase

Lemur tyrosine kinase 3 (LMTK3) is oncogenic in various cancers. In breast cancer, LMTK3 phosphorylates and modulates the activity of estrogen receptor-α (ERα) and is essential for the growth of ER-positive cells. LMTK3 is highly expressed in ER-negative breast cancer cells, where it promotes invasion via integrin β1. LMTK3 abundance and/or high nuclear expression have been linked to shorter disease free and overall survival time in a variety of cancers, supporting LMTK3 as a potential target for anticancer drug development. We sought to identify small molecule inhibitors of LMTK3 with the ultimate goal to pharmacologically validate this kinase as a novel target in cancer. We used a homogeneous time resolve fluorescence (HTRF) assay to screen a collection of mixture-based combinatorial chemical libraries containing over 18 million compounds. We identified several cyclic guanidine-linked sulfonamides with sub-micromolar activity and evaluated their binding mode using a 3D homology model of the LMTK3 K_D.

The lncRNA MIR2052HG regulates ERα levels and aromatase inhibitor resistance through LMTK3 by recruiting EGR1

Background

Our previous genome-wide association study using the MA.27 aromatase inhibitors adjuvant trial identified SNPs in the long noncoding RNA MIR2052HG associated with breast cancer-free interval. MIR2052HG maintained ERα both by promoting AKT/FOXO3-mediated ESR1 transcription and by limiting ubiquitin-mediated ERα degradation. Our goal was to further elucidate MIR2052HG’s mechanism of action.

Methods

RNA-binding protein immunoprecipitation assays were performed to demonstrate that the transcription factor, early growth response protein 1 (EGR1), worked together with MIR2052HG to regulate that lemur tyrosine kinase-3 (LMTK3) transcription in MCF7/AC1 and CAMA-1 cells. The location of EGR1 on the LMTK3 gene locus was mapped using chromatin immunoprecipitation assays. The co-localization of MIR2052HG RNA and the LMTK3 gene locus was determined using RNA-DNA dual fluorescent in situ hybridization. Single-nucleotide polymorphisms (SNP) effects were evaluated using a panel of human lymphoblastoid cell lines.

Results

MIR2052HG depletion in breast cancer cells results in a decrease in LMTK3 expression and cell growth. Mechanistically, MIR2052HG interacts with EGR1 and facilitates its recruitment to the LMTK3 promoter. LMTK3 sustains ERα levels by reducing protein kinase C (PKC) activity, resulting in increased ESR1 transcription mediated through AKT/FOXO3 and reduced ERα degradation mediated by the PKC/MEK/ERK/RSK1 pathway. MIR2052HG regulated LMTK3 in a SNP- and aromatase inhibitor-dependent fashion: the variant SNP increased EGR1 binding to LMTK3 promoter in response to androstenedione, relative to wild-type genotype, a pattern that can be reversed by aromatase inhibitor treatment. Finally, LMTK3 overexpression abolished the effect of MIR2052HG on PKC activity and ERα levels.

Conclusions

Our findings support a model in which the MIR2052HG regulates LMTK3 via EGR1, and LMTK3 regulates ERα stability via the PKC/MEK/ERK/RSK1 axis. These results reveal a direct role of MIR2052HG in LMTK3 regulation and raise the possibilities of targeting MIR2052HG or LMTK3 in ERα-positive breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1130-3) contains supplementary material, which is available to authorized users.

The LMTK-family of kinases: Emerging important players in cell physiology and pathogenesis

Lemur Tail (former tyrosine) Kinases (LMTKs) comprise a novel family of regulated serine/threonine specific kinases with three structurally and evolutionary related members. LMTKs exercise a confusing variety of cytosolic functions in cell signalling and membrane trafficking. Moreover, LMTK2 and LMTK3 also reside in the nucleus where they participate in gene transcription/regulation. As a consequence, LMTKs impact cell proliferation and apoptosis, cell growth and differentiation, as well as cell migration. All these fundamental cell behaviours can turn awry, most prominently during neuropathologies and tumour biogenesis. In cancer cells, LMTK levels are often correlated with poor overall prognosis and therapy outcome, not least owned to acquired drug resistance. In brain tissue, LMTKs are highly expressed and have been linked to neuronal and glia cell differentiation and cell homeostasis. For one member of the LMTK-family (LMTK2) a role in cystic fibrosis has been identified. Due to their role in fundamental cell processes, altered LMTK physiology may also warrant a hitherto unappreciated role in other diseases, and expose them as potential valuable drug targets. On the backdrop of a compendium of LMTK cell functions, we hypothesize that the primary role of LMTKs may dwell within the endocytic cargo recycling and/or nuclear receptor transport pathways.

Effect of hMLH1, hMSH2, hMSH6, integrin β1, and Ki-67 expression on prognosis of colorectal cancer

AIM

To investigate the expression of hMLH1, hMSH2, hMSH6, integrin β1, and Ki-67 in colorectal cancer and to analyze their effect on the prognosis of this malignancy.

METHODS

One hundred and sixty-two tumor specimens of colorectal cancer patients treated in Jinhua Hospital of Jinhua University were collected, and immunohistochemical staining was used to determine the expression of hMLH1, hMSH2, hMSH6, integrin β1, and Ki-67 in the specimens. The results were analyzed statistically.

RESULTS

Among 162 specimens, 36 were found to have missing expression of hMLH1, hMSH2, and hMSH6, with a deletion rate of 22.22%. The expression of MMR protein was significantly associated with tumor diameter (P = 0.0005), Dukes stage (P = 0.0248), family history of tumor (P = 0.0042), and lymph node metastasis (P = 0.0014). The positive expression of integrin β1 was significantly associated with Dukes stage (P = 0.0002), and the positive expression of Ki-67 was significantly associated with Dukes stage (P = 0.0002) and lymph node metastasis (P = 0.0111). Loss of MMR protein expression and positive expression of integrin β1 and Ki-67 were significantly associated with Dukes stage (P = 0.006) and lymph node metastasis (P = 0.023). The 5-year survival rate was 88.89% in the deficient mismatch repair group and 59.52% in the proficient mismatch repair group, and the difference was statistically significant (P = 0.0010). The 5-year survival rate was significantly lower in the integrin β1 positive group than in the integrin β1 negative group (59.69% vs 90.91%, P = 0.0007). The 5-year survival rate was also significantly lower in the Ki-67 positive group than in the Ki-67 negative group (63.27% vs 93.33%, P = 0.0192).

CONCLUSION

The expression of MMR protein, integrin β1, and Ki-67 is statistically correlated with Dukes stage and lymph node metastasis in colorectal cancer, and all the three factors are related to the prognosis of patients: loss of MMR protein expression and negative expression of integrin β1 and Ki-67 are associated with better prognosis and higher 5-year survival rate.

LMTK3 is essential for oncogenic KIT expression in KIT-mutant GIST and melanoma

Certain cancers, including gastrointestinal stromal tumor (GIST) and subsets of melanoma, are caused by somatic KIT mutations that result in KIT receptor tyrosine kinase constitutive activity, which drives proliferation. The treatment of KIT-mutant GIST has been revolutionized with the advent of KIT-directed cancer therapies. KIT tyrosine kinase inhibitors (TKI) are superior to conventional chemotherapy in their ability to control advanced KIT-mutant disease. However, these therapies have a limited duration of activity due to drug-resistant secondary KIT mutations that arise (or that are selected for) during KIT TKI treatment. To overcome the problem of KIT TKI resistance, we sought to identify novel therapeutic targets in KIT-mutant GIST and melanoma cells using a human tyrosine kinome siRNA screen. From this screen, we identified lemur tyrosine kinase 3 (LMTK3) and herein describe its role as a novel KIT regulator in KIT-mutant GIST and melanoma cells. We find that LMTK3 regulated the translation rate of KIT, such that loss of LMTK3 reduced total KIT, and thus KIT downstream signaling in cancer cells. Silencing of LMTK3 decreased cell viability and increased cell death in KIT-dependent, but not KIT-independent GIST and melanoma cell lines. Notably, LMTK3 silencing reduced viability of all KIT-mutant cell lines tested, even those with drug-resistant KIT secondary mutations. Furthermore, targeting of LMTK3 with siRNA delayed KIT-dependent GIST growth in a xenograft model. Our data suggest the potential of LMTK3 as a target for treatment of patients with KIT-mutant cancer, particularly after failure of KIT TKIs.

LMTK3 confers chemo-resistance in breast cancer

Lemur tyrosine kinase 3 (LMTK3) is an oncogenic kinase that is involved in different types of cancer (breast, lung, gastric, colorectal) and biological processes including proliferation, invasion, migration, chromatin remodeling as well as innate and acquired endocrine resistance. However, the role of LMTK3 in response to cytotoxic chemotherapy has not been investigated thus far. Using both 2D and 3D tissue culture models, we found that overexpression of LMTK3 decreased the sensitivity of breast cancer cell lines to cytotoxic (doxorubicin) treatment. In a mouse model we showed that ectopic overexpression of LMTK3 decreases the efficacy of doxorubicin in reducing tumor growth. Interestingly, breast cancer cells overexpressing LMTK3 delayed the generation of double strand breaks (DSBs) after exposure to doxorubicin, as measured by the formation of γH2AX foci. This effect was at least partly mediated by decreased activity of ataxia-telangiectasia mutated kinase (ATM) as indicated by its reduced phosphorylation levels. In addition, our RNA-seq analyses showed that doxorubicin differentially regulated the expression of over 700 genes depending on LMTK3 protein expression levels. Furthermore, these genes were found to promote DNA repair, cell viability and tumorigenesis processes / pathways in LMTK3-overexpressing MCF7 cells. In human cancers, immunohistochemistry staining of LMTK3 in pre- and post-chemotherapy breast tumor pairs from four separate clinical cohorts revealed a significant increase of LMTK3 following both doxorubicin and docetaxel based chemotherapy. In aggregate, our findings show for the first time a contribution of LMTK3 in cytotoxic drug resistance in breast cancer.

Identification and analysis of mutational hotspots in oncogenes and tumour suppressors

Background

The key to interpreting the contribution of a disease-associated mutation in the development and progression of cancer is an understanding of the consequences of that mutation both on the function of the affected protein and on the pathways in which that protein is involved. Protein domains encapsulate function and position-specific domain based analysis of mutations have been shown to help elucidate their phenotypes.

Results

In this paper we examine the domain biases in oncogenes and tumour suppressors, and find that their domain compositions substantially differ. Using data from over 30 different cancers from whole-exome sequencing cancer genomic projects we mapped over one million mutations to their respective Pfam domains to identify which domains are enriched in any of three different classes of mutation; missense, indels or truncations. Next, we identified the mutational hotspots within domain families by mapping small mutations to equivalent positions in multiple sequence alignments of protein domains We find that gain of function mutations from oncogenes and loss of function mutations from tumour suppressors are normally found in different domain families and when observed in the same domain families, hotspot mutations are located at different positions within the multiple sequence alignment of the domain.

Conclusions

By considering hotspots in tumour suppressors and oncogenes independently, we find that there are different specific positions within domain families that are particularly suited to accommodate either a loss or a gain of function mutation. The position is also dependent on the class of mutation. We find rare mutations co-located with well-known functional mutation hotspots, in members of homologous domain superfamilies, and we detect novel mutation hotspots in domain families previously unconnected with cancer. The results of this analysis can be accessed through the MOKCa database (http://strubiol.icr.ac.uk/extra/MOKCa).

LMTK3 escapes tumour suppressor miRNAs via sequestration of DDX5

Lemur tyrosine kinase-3 (LMTK3) plays an important role in cancer progression and is associated with breast, lung, gastric and colorectal cancer. MicroRNAs (miRNAs) are small endogenous non-coding RNAs that typically repress target genes at post-transcriptional level and have an important role in tumorigenesis. By performing a miRNA expression profile, we identified a subset of miRNAs modulated by LMTK3. We show that LMTK3 induces miR-34a, miR-196-a2 and miR-182 levels by interacting with DEAD-box RNA helicase p68 (DDX5). LMTK3 binds via DDX5 to the pri-miRNA of these three mature miRNAs, thereby sequestrating them from further processing. Ectopic expression of miR-34a and miR-182 in LMTK3-overexpressing cell lines (MCF7-LMTK3 and MDA-MB-231-LMTK3) inhibits breast cancer proliferation, invasion and migration. Interestingly, miR-34a and miR-182 directly bind to the 3'UTR of LMTK3 mRNA and consequently inhibit both its stability and translation, acting as tumour suppressor-like miRNAs. In aggregate, we show that LMTK3 is involved in miRNA biogenesis through modulation of the Microprocessor complex, inducing miRNAs that target LMTK3 itself.

Rapid immunoprecipitation mass spectrometry of endogenous proteins (RIME) for analysis of chromatin complexes

Rapid immunoprecipitation mass spectrometry of endogenous protein (RIME) is a method that allows the study of protein complexes, in particular chromatin and transcription factor complexes, in a rapid and robust manner by mass spectrometry (MS). The method can be used in parallel with chromatin immunoprecipitation-sequencing (ChIP-seq) experiments to provide information on both the cistrome and interactome for a given protein. The method uses formaldehyde fixation to stabilize protein complexes. By using antibodies against the endogenous target, the cross-linked complex is immunoprecipitated, rigorously washed, and then digested into peptides while avoiding antibody contamination (on-bead digestion). By using this method, MS identification of the target protein and several dozen interacting proteins is possible using a 100-min LC-MS/MS run. The protocol does not require substantial proteomics expertise, and it typically takes 2-3 d from the collection of material to results.